Crude oils predominantly contain hydrocarbons, with sulfur, nitrogen, oxygen, and metals being minor constituents. While it is desirable to recover the hydrocarbon constituents in their pure form, it is difficult to isolate pure products because most of the minor constituents occur in combination with carbon and hydrogen. Separation of impurities, such as those listed above, from the hydrocarbons generally consumes time, chemicals, energy, and money. Therefore, one goal of the petroleum processing industry is to optimize impurity-removal procedures, equipment, and resources in order to eliminate those impurities that have the most degrading effect on the end products.
A common impurity encountered in hydrocarbon processing is sulfur. The presence of sulfur in hydrocarbon products generally increases the corrosive characteristics thereof, and sulfur forms harmful and noxious reaction products upon combustion. Consequently, measures are taken to either reduce the amount of sulfur or to render the sulfur-containing compounds inoffensive. A common method for treating petroleum to reduce the degrading effects of sulfur is chemical processing to “sweeten” sulfur compounds contained in the particular fractions, e.g., mercaptans that are designated by the formula R—SH. “Sweetening” denotes that mercaptan sulfur compounds are converted to less objectionable disulfide compounds, e.g., R—S—S—R, R—S—S—R′, etc. One particular process known in the art is the sweetening of petroleum products such as kerosene by the Merox process, which is available from UOP LLC of Des Plaines, Ill., USA.
In order to sweeten a petroleum product, a caustic solution, such as sodium hydroxide or potassium hydroxide, is generally first used to convert the mercaptan compounds to the ionic state, RS−. The caustic solution is also helpful in that it removes naphthenic acids and other organic acids in general such as phenolic acids, and other sulfur compounds from refined petroleum products and petroleum distillate. Various processes for regenerating the caustic solutions and apparatus for same are disclosed in the prior art. For example, U.S. Pat. Nos. 8,597,501 and 7,326,333 disclose such exemplary processes and apparatus. While these processes and apparatuses are effective for their intended purposes, in some processes, it may not be necessary for a total reduction of sulfur compounds. More specifically, the presence of some sulfur compounds, such as disulfides in the sweetened hydrocarbon stream, may be acceptable for various refiners. Accordingly, some of the units and vessels associated with a caustic regeneration may be superfluous or unnecessary for some refiners.
Therefore, it would be desirable to have processes and systems which allow for the regeneration of a caustic solution without requiring all of the equipment typically associated with the processing of such streams. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.